Isolation barrier and switching performance
The CNY173W delivers 5300Vrms isolation between input and output, a rating suited for reinforced isolation in mains-referenced circuits — the 6-DIP package provides the creepage distance to sustain this voltage without tracking. Switching is characterised by 1µs rise and 2µs fall times, with turn-on at 2µs and turn-off at 3µs typical — fast enough for isolated feedback in 50/60 Hz power supplies or low-speed logic interfaces. The transistor-with-base output allows the designer to bias the base for optimised switching speed or to use the phototransistor in a common-base configuration, trading gain for bandwidth.
Current transfer ratio and drive margins
CTR is specified at 100% minimum and 200% maximum, both at If=10mA — this guarantees the output transistor saturates with a 10mA LED drive, leaving margin for LED ageing over temperature. Maximum forward current is 100 mA, and the typical forward voltage is 1.35V — the LED can be driven directly from a 3.3V logic output through a series resistor without a separate driver stage. Output saturation voltage is 300mV max at the rated collector current, keeping the logic-low level well within TTL thresholds when the output is pulled up to 5V through a resistor.
For a BOM line that depends on the 5300Vrms isolation and through-hole DIP-6 footprint, the CNY173W remains orderable as long as surplus inventory exists; a board redesign would be required to migrate to a different package or isolation class.